1. Field of the Invention
This invention relates to a focus adjusting device in a binocular.
2. Description of the Prior Art
A conventional focus adjusting device in a binocular is generally provided with a rotating knob at the center portion of the binocular and the rotating operation of the rotating knob moves an eyepiece portion for focus adjusting operation.
In recent years a focus adjusting device for example, as shown in U.S. Pat. No. 4,066,329, has been proposed for the purpose of being capable of effecting momentary focus adjusting for responding to a quick aiming motion, the focus adjusting device being designed in such a manner that a winglike portion for operation is provided instead of the rotating knob; a pin which is bounded to move in the direction of the movement of an ocular is snugly fitted into the cam groove of the winglike portion; and the swing motion of the winglike portion causes the ocular integral with the pin to be moved. However, in the proposed focus adjusting device, an inclination of the cam groove is considerably steep and therefore, when an observer desires to observe by use of a binocular and his eyes press on and are in contact with the eyepiece portion thereof, the eyepiece portion often moves and the in-focus position shifts. To avoid such movement of the eyepiece portion, a friction member such as a spring washer is required. However, use of the friction member unhappily prevents smooth rotation of the winglike portion.